Method of producing a photograph in glass



United States Patent f METHOD OF PRODUCING A PHOTOGRAPH 1N GLASS HowardG. Ross and Frederic W. Schuler, Corning, N.Y., assignors to CorningGlass Works, Corning, N.Y., a corporation of New York No Drawing.Application September 29, 1954 Serial No. 459,201

16 Claims. (CI. 96-34) This invention relates to the production of apermanent, two-dimensional, photographic image in glass.

Such an image heretofore has been produced by the method disclosed inthe pending application Serial No. 324,415, filed December 5, 1952, byStanley Donald Stookey, now Patent No. 2,732,298, which comprisesforming on the surface of a silicate glass containing an alkali metaloxide a chemically fixed, photographic colloidal silver image, heatingthe glass together with the image in the presence of an oxidizing mediumfor a time sufiicient to oxidize and ionize the silver and to causemigration of silver ions into the glass, and reducing the migratedsilver ions to metallic particles while heating the glass in thepresence of a reducing medium. The reduced silver particles produce ayellow to brown coloration known as a silver stain which forms a sharplydelineated image in the surface of the glass.

In the prior method the photographic silver image initially present onthe glass surface is produced in the conventional manner by the exposureand chemical development of an emulsion comprising a photosensitivesilver halide dispersed in an organic medium. Such emulsion may beapplied as a coating to the surface of the glass before its exposure anddevelopment or it may be transferred to the glass after its exposure anddevelop ment, for example as stripping film.

In utilizing such a photosensitive emulsion, however, it is difficult tomaintain all parts of the silver image exactly in their originaldimensional relationship with each other on account of a tendency forone portion of the image to change its position on the glass relative toanother portion during the developmental manipulations and/ or theburning-off of the organic material of the emulsion. Even a very minorstretching or contraction of the emulsion during its development ortransfer or resulting from the burning of the organic material betweenthe silver and the glass may result in a slight distortion of the imagesufiicient to render it unsuitable for articles requiring greatdimensional accuracy such as reticles and scales.

Moreover, the prior method is dependent upon the photosensitivity of thesilver halides and is limited to a final image comprising a silverstain. It therefore cannot be utilized to produce a similar imageconsisting of the equally well known copper stain, because nophotosensitive compound of copper is known. A copper stain is desirablefor some purposes, because it produces a difierent coloration than thesilver stain.

It is an object of the present invention to provide a method by which atwo-dimensional image consisting of either a silver stain or a copperstain or a combined silver and copper stain can be produced in glassWith greater accuracy than was heretofore possible. The new method isindependent of the photosensitivity of a salt of the metal used toproduce the stain and the initial metallic image can be formed inintimate direct contact with the glass, wherefore its dimensionalaccuracy can readily be maintained.

2,904,432 Patented Sept. 15, 1959 Broadly the new method according tothe invention comprises forming directly in contact with a silicateglass article containing an alkali metal oxide a continuous metallicfilm of silver or copper, or both silver and copper, in a patterncorresponding to the desired image heating the article in the presenceof an oxidizing medium comprising air at a temperature and for a timesufficient to oxidize and ionize the metal image and to cause migrationof the ions into the glass, and reducing the migrated ions to metallicparticles while heating the article in the presence of a reducingmedium.

Preferably the desired image is delineated in the metallic film bycovering it with a coating of a photosensitive resist capable of beingrendered insoluble by. exposure to short wave radiations (less than 400millimicrons), such as ultraviolet radiations, exposing a portion ofsuch coating to said radiations in a pattern corresponding to thedesired image to render such portion insoluble, dissolving and removingthe unexposed portion of the coating to lay bare the metal filmthereunder, and dissolving and removing the bared metal while leavingintact the metal underlying the insoluble portion of the coating, saidresidual coating being removed by oxidation and combustion when theglass is subsequently heated in the above described manner.

The new method is effective only in glasses containing an alkali metaloxide because the staining of glass by silver and copper depends uponthe exchange of silver and copper ions in contact with the heated glassfor alkali metal ions in the glass. Insofar as we know, the glass shouldbe a silicate glass. The general composition of a suitable glass is nototherwise critical and any practicable silicate glass containing analkali metal oxide may be utilized for carrying out the invention.Advantageously glasses of the soda-lime-silicate type such as thosedescribed in United States Patent No. 1,369,988 or of the low-expansionborosilicate type such as those described in United States Patent No.1,304,623 may be used. It is immaterial whether or not the glass itselfis photosensitive because the present method is independent of thephotosensitivity of the glass. However, non-photosensitive glasses arepreferred as being cheaper and less liable to develop undesiredcoloration.

The metallic film may be deposited on the glass by various known methodssuch as the chemical precipitation from a solution of a salt of themetal. One such method for silver, the Brashear method, is so well knownand so widely published in texts relating to the production of silvermirrors as to need no discussion here.

A method for the deposition of a copper mirror is described in anarticle entitled The Chemical Deposition of Copper Mirrors on Glass, byMarboe and Weyl, Glass Industry, vol. 26, page 119 (1945).

An alternative method of depositing a film of silver or copper on theglass is the well known method of evaporating the metal by heat in avacuum and allowing the metal vapor to condense on the surface of theglass which is placed in the vicinity of the evaporator in the vacuum,as is described for example in Patent No. 2,413,605. A film containingboth silver and copper may be formed, if desired, by thus evaporatingone metal on to the glass and then evaporating the other metal over thefirst, or by evaporating a suitable alloy of both metals. A layer of oneof the metals can also be formed by chemical deposition and asuperimposed layer of the other can then be formed by evaporation.Superimposed layers can also be formed by electroplating by making thefirst deposited metal the cathode in a suitable electrolyte.

To delineate the desired image in the metallic film a coating of aphotosensitive resist, referred to as a photoresist, is applieduniformly over the film. This usually comprises a soluble organicmaterial or mixture of materials, which polymerizes and becomesinsoluble when exposed to visible actinic or short wave radiations. Byway of example the following are some Well known photo-resists which aresuitable for the present purpose:

Bi'chromated gelatin or fish glue, which is composed of either gelatinor fish glue and contains a photosensitive bichromate, is extensivelyused. It is initially soluble in Water but becomes insoluble thereinwhen exposed to ultraviolet radiations.

' Bichromated albumin, composed of albumin and a photosensitivebichromate, is utilized in a similar manner but after exposure it shouldbe coated with a greasy ink, such as printers ink, to render the exposedportion hydrophobic, the unexposed portion remaining unaffected andsoluble in water.

Polyvinyl alcohol, which is inherently polymerizable by ultravioletradiations, may be used Without addition of a photosensitive element.Since it is water soluble before exposure, Water may be used as thedeveloper. It is susceptible to oxidation if exposed to the air morethan momentarily.

Polyvinyl acetate, also polymerizes on exposure to ultravioletradiations and the exposed portions can also be developed by water Gilof Judea, which is a mixture of asphalt and lavender oil, alsopolymerizes on exposure to ultraviolet radiations, but is developed bymeans of a light mineral oil as a developer.

A commonly used photo-resist comprises an organic monomer described inPatent No. 2,610,120, which is polymerizable by ultraviolet radiations.It is sold under the trade name KPR by the Eastman Company of Rochester,New York. Trichlorethylene is used as its developer.

The desired image is formed in the coating of photoresist in theconventional manner by exposing the coating of photo-resist in theconventional manner by exposing the coating to a suitable source ofshort-wave radiations, such as a carbon or mercury are, projectedthrough a photographic transparency, preferably placed in contact withthe photo-resist. Development of the image occurs when the photo-resistthereafter is treated with the appropriate solvent to dissolve andremove the unexposed or soluble portion thereof.

The type of image produced depends upon the photographic transparencyemployed. A fulltone image, such as a reticle, scale, line drawing,silhouette and the like, is produced by using a transparency made byphotographing a drawing of the desired object. A halftone image, such asa portrait or a landscape, is reproduced by using a conventionalhalf-tone transparency made by photographing the subject or areproduction thereof through a half-tone screen. A negative transparencyproduces a positive image in the photo-resist and also in the glasswhile a positive transparency produces a negative image By dissolvingand removing the metal film from the glass Wherever the overlyingcoating of the photo-resist has been removed a replica of the image isreproduced in the metal remaining in contact with the glass. For thispurpose any dilute solvent of the metal, such as dilute nitric acid or adilute solution of ferric nitrate, may be used provided it does notdissolve or objectionably react with the photo-resist.

After the image has thus been delineated in the metal, the glass articleis heated at a temperature and for a time sufficient to oxidize andeliminate the residual photoresist and to oxidize and ionize the metalimage and cause migration of the ions into the glass. Such reactionsoccur at a practicable rate (from one to six hours) at temperatureshaving a minimum about 125 C. below the strain point of the glass. Thereaction is more rapid at higher temperatures and requires only one tofive minutes 'at the maximum temperature which should be sufficientlybelow the softening point of the glass to avoid dis- 4 tortion thereof.(As used herein, strain point means that temperature at which theviscosity of the glass is 10 poises and softening point is thattemperature at which the viscosity of the glass is 10 poises.) While theminimum and maximum temperatures at which the reaction can occur varywith the strain point and the softening point of the glass, thepracticable temperature will not be less than about 400 C. nor more thanabout 700 C.

The ion exchange or migration of the metal ions into the glass mayadvantageously be facilitated by applying to the glass and over themetal image a coating of an argillaceous material, such as preferablyocher, before heating it. The argillaceous material, which is moreeffective if finely divided, is applied as a paste or slurry with wateror other vehicle such as an oil or volatile organic liquid. Suchtreatment is particularly effective if the metal comprises silver. Whenthe metal is copper the argillaceous material is more effective if itcontains a sulfide such as ferric or ferrous sulfide.

In lieu of an argillaceous coating, the presence of up to about 25% byvolume of 50 in the air in contact with the glass and the metal, whilethey are being heated to cause oxidation and migration of the metal ionsinto the glass, facilitates or increases such ion migration for bothsilver and copper; larger proportions of S0 in the air lessen or preventoxidation and migration of the metal ions. The beneficial effect 'of S0is independent of the presence of the argillaceous coating but is notinhibited thereby.

The oxidation, ionization and ion migration, particularly of silver mayfurther be increased by the presence in the reaction zone of one or moreof the salts, ferric sulfate, ferrous sulfate or aluminum sulfate eitheralone or, as is referable, in admixture with the argillaceous material.

The migrated metal ions change the refractive index of the glass usuallysufiicie'ntly to produce at least a faintly visible image, which in thecase of silver is usually of a yellowish color due to spontaneousconversion or reduction of a small portion of the silver ions in theglass to metallic particles. In the case of copper the glass remainscolorless until heated in the presence of a reducing medium unless theglass is a borosilicate, such as the low expansion borosilicate referredto above, in which case the glass is spontaneously colored yellow by thecopper.

The complete reduction of the migrated metal ions and the resultingdevelopment of the maximum coloration of the image in the glass thereby(brown to black in the case of silver, red to black in the case ofcopper, and black when both are present) occurs when the glass is heatedunder reducing conditions, preferably in an atmosphere containing areducing gas such as hydrogen, carbon monoxide, or methane.Advantageously this may comprise continuing the heating in the aboverecited temperature range after the migration of the metal ions into theglass has taken place and displacing the atmospheric air With thereducing gas.

Since the metal ions normally migrate into the glass a distance of onlya few microns, the final image therein is substantially two-dimensional.v

if desired, the steps of (the above-described method may be carried outin a different sequence with substantially the same result. For thispurpose the coating of the photo-resist is applied as the first stepdirectly to the glass and an image is formed therein by exposure toshort-wave radiations through a photographic transparency. In this case,however, the image in the photoresist must be the reverse of the desiredimage and, if a positive image in the glass is desired, a negative imageshould be formed in the photo-resist. That is to say, a positivetransparency is utilized to produce a positive image in the glass. I

The image in the photo-resist is then developed by dissolving andremoving the unexposed portion of the coating to lay bare the glassthereunder in a pattern corresponding to the desired final image Whileleaving the exposed portion of the coating on the glass in a patterncorresponding to the reversed image.

The thinmetallic film of silver or copper or both silver and copper isthen deposited uniformly on the bared glass and over the residualportion of the photo-resist and the glass is thereafter heated in themanner described above.

In such method the metal in contact with the bared glass forms thepattern of the desired image, but the metal over the residual portion ofthe photo-resist forms a reversed image which is not in contact with theglass. During the subsequent heating. of the glass the metal which doesnot contact the glass is ineffective and the stained image is producedin the glass only by the metal which is in contact therewith.

Example 1 On one face of a plate of soda-limesilicate glass approximately one foot square a silver mirror was formed by theconventional wet chemical process. A coating of a photo-resistcomprising an ultraviolet-polymerizable organic monomer soluble intrichlorethylene was applied over the metal film and was exposed forapproximately three minutes at a distance of about 1 foot to an 800 wattnew quartz mercury are through a negative photographic transparency madeby photographing a line drawing depicting a scale. (After long use theultraviolet emission of such an arc is decreased and a longer exposure,up to 30 minutes, may be required.) Following such exposure the glassplate was treated with trichlorethylene to dissolve the unexposedportion of the photoresist and to lay bare the metal film beneath it.The exposed portion, representing the lines of the drawing and beinginsoluble, was undissolved. The plate with the developed image was thentreated with a aqueous solution of ferric nitrate which dissolved thebared silver within a few minutes leaving the portion of the silver filmwhich was protected by the undissolved portion of the photo-resist.

A coating of a paste of ocher and water containing about 10% by weightof ferric sulfate was then applied and the glass plate was heated slowlyin air to about 650 C. Where it was held for about five minutes, afterwhich it was heated in an atmosphere of 92% nitrogen and 8% hydrogen byvolume and then cooled and the residual material was wiped off. An imageof the line drawing remained as a permanent dark brown stain in thesurface of the glass.

Example 2 A plate of soda-lime-silicate glass was provided with a thinfilm of copper by the conventional method of evaporating the metal anddepositing it on the glass in a vacuum. A coating of the photo-resistutilized in EX- ample l was applied over the copper film and an imagewas formed therein and developed as in Example 1. The area of the metallaid bare by such development of the image in the photo-resist wasremoved from the glass by treating the plate with a aqueous solution ofnitric acid leaving a copper replica of the original image beneath theinsoluble residue of the photo-resist.

A paste of ocher and water containing about 5% each of finely dividedferrous sulfide and ferric sulfate was applied over such image and theglass plate was slowly heated in air in an electrically heated mufile toabout 600 C. where it was held for about ten minutes. The atmosphere ofthe mufile was then displaced by a nonexplosive mixture of 92% nitrogenand 8% hydrogen and heating at 600 C. was continued for twenty minutes.An image of a dark red color was thereby produced in the glass.

Example 3 A small plate of soda-lime-silicate glass was coated with amixture of copper and silver by evaporating the metals simultaneouslyfrom individual molybdenum containers electrically heated in a vacuumand condensing the metal vapors together on the glass which Was placedin the evacuated space near the evaporators. A coating of thephoto-resist utilized in Example 1 was applied over the metal film andan image was formed therein by exposing the coating for about threeminutes at a distance of about one foot to a quartz mercury arc througha negative photographic transparency and thereafter treating it withtrichlorethylene to remove the unexposed portion and to lay bare themetal beneath, the bare portion of the metalbeing subsequently dissolvedby dipping the plate into 15% aqueous nitric acid. The plate was thencoated with ocher and heated as in Example 2. The positive imageproduced in the glass was practically black in color;

Example 4 A plate of soda-lime-silicate glass was provided with auniform coating of the photo-resist utilized in Example 1 and an imagewas formed and developed therein by exposing the coating for about threeminutes at a distance of one foot to a quartz mercury are through anegative photographic transparency and thereafter treating it withtrichlorethylene to remove the unexposed portion. In this case the baredarea of the glass corresponded to the desired image.

A silver mirror was then deposited by the chemical process over theentire face of the plate, that is, over the residual photo-resist andover the bared portion of the glass representing the desired image.While the silver adhered well to the bared glass, it could easily berubbed off from the photo-resist.

The surface of the plate was then covered with a paste of ocher andwater containing about 10% by weight of ferric sulfate and the plate washeated slowly in air to about 600 C. where it was held for about tenminutes followed by about twenty minutes heating in a reducingatmosphere as in Example 2, after which it was cooled and the residualmaterial was wiped off. The silver which was in contact with the baredportion of the glass formed therein a permanent dark-brown,two-dimensional, negative image but the silver overlying the exposedportion of the photo-resist did not adhere to the glass nor stain it butwas wiped olf with the other residual material.

Example 5 By means of the new method a plurality of images of differentcolors may be formed in a single glass article. For instance a thin filmof copper is deposited on a plate of low expansion borosilicate glassand an image is formed therein by applying thereover a coating of aphoto-resist comprising bichromated gelatin, exposing the photo-resistthrough a photographic transparency, developing an image therein whilelaying bare the copper film comprising the background of the image, anddissolving the bared copper in accordance with the procedure of Example2. A film of silver is then deposited over the entire surface byevaporation in a vacuum, a coating of the photo-resist is appliedthereover and the coating is exposed through a different photographictransparency, an image is developed therein and the silver laid bare bysuch "development is dissolved as in Example 1. Thereafter the glass iscoated with ocher and heated in the manner described in Example 2. Suchprocedure reproduces in the glass in a brown color the image formed inthe silver film and in a red color the image formed in the copper film.Where the silver image was superimposed on the copper image the color ofthe combination is brown to black.

We claim:

1. The method of producing a permanent, two-dimen sional, photographicimage in glass, which comprises forming directly in contact with asilicate glass article containing an alkali metal oxide 8, continuousmetallic film of at least one metal selected from the group consistingof silver and copper in a pattern corresponding to the desired image,heating the article under oxidizing conditions in air at a temperatureand for a time sufiicient to oxidize and ionize the metal image and tocause migration of the ions into the glass in exchange for the alkalimetal ions therein, and heating the article in a reducing atmosphere toreduce the migrated ions to metallic particles dispersed in and coloringthe surface of the glass.

2. The method of producing a permanent, two-dimer:v

sional, photographic image in glass, which comprises depositing on thesurface of a silicate glass article containing an alkali metal oxide acontinuous metallic film of at least one metal selected from the groupconsisting of silver and copper, covering such film with a coating of alight-sensitive resist capable of being rendered insoluble by exposureto short-wave radiations, exposing a portion of the coating to saidradiations in a pattern corresponding to the desired image to rendersuch portion insoluble, dissolving and removing the unexposed portion ofthe coating to lay bare the metal film thereunder, dissolving andremoving the hared metal while leaving intact the metal underlying theinsoluble portion of the coating, heating the article under oxidizingconditions in air at a temperature and for a time sufficient to removethe insoluble portion of the coating and to oxidize and ionize theunderlying metal and to cause migration of the ions into the glass inexchange for the alkali metal ions there in, and heating the article ina reducing atmosphere to reduce the migrated ions to metallic particlesdispersed in and coloring the surface of the glass.

3. The method of claim 2 in which the metallic film consists of silver.

4. The method of claim 2 in which the metallic film consists of copper.

5. The method of claim 2 in which the said article is heated underoxidizing conditions in air containing up to 25% by volume of S 6. Themethod of claim 2 in which the reducing atmosphere contains a gasselected from the class consisting of hydrogen, carbon monoxide, andmethane.

7. The method of claim 6 in which the gas is composed of 8% hydrogen and92% nitrogen.

8. The method of claim 2 in which a layer of ocher is applied over atleast the insoluble portion of the coating before the article is heated.

9. The method of claim 8 in which the layer contains a sulfate selectedfrom the group consisting of ferric sulfate, ferrous sulfate andaluminum sulfate.

10. The method of producing a permanent, tw'odimensional, photographicimage in glass, which comprises applying to the surface of a silicateglass containing an alkali metal oxide a coating of a light-sensitiveresist capable of being rendered insoluhle by exposure to shortwaveradiations, exposing a portion of the coating to said radiations in apattern corresponding to the reverse of the desired image to render suchportion insoluble, dissolving and removing the unexposed portion or thecoating to lay bare the glass thereunder, depositing uniformly on thebared glass and over the residual portion of the light-sensitive resista continuous metallic film of at least one metal selected from the groupconsisting of silver and copper, heating the glass under oxidizing conditions in air at a temperature and for a time sufiicient to remove theresidual portion of the coating together with the metal thereover and tooxidize and ionize the metal which is in contact with the glass and tocause migration of the ions into; the glass, and heating the glass in areducing atmosphere to reduce the migrated ions to metallic particlesdispersed in and coloring the surface of glass.

11. The method of claim 10 in which the metallic film consists ofsilver.

12. The method of claim 10 in which the metallic film consists ofcopper.

13. The method of claim 10 in which the said article is heated underoxidizing conditions in air containing up to 25% by volume of S0 14. Themethod of claim 10 in which the reducing atmosphere contains a gasselected from the class consisting of hydrogen, carbon monoxide, andmethane.

15. The method of claim 14 in which the reducing atmosphere is composedof 8% hydrogen and 92% nitrogen.

16. The method of claim 10 in which a layer of ooher containing ferroussulfide is applied over the metal film before the glass is heated.

References Cited in the file of this patent UNITED STATES PATENTS1,884,665 Greiner Oct. 25, 1932 1,994,483 Ott Mar. 19, 1935 2,233,622Lytle Mar. 4, 1941 2,279,567 Holman Apr. 14, 1942 2,357,913 SigfordSept. 12, 1944 2,399,799 Guellich May 7, 1946 2,435,889 Kerridge Feb.10, 1948 2,447,836 Beeber et al. Aug. 24, 1948 2,628,927 Colbert et al.Feb. 17, 1953 2,649,387 Parsons et al. Aug. 18, 1953 2,659,665 Parsonset al Nov. 17, 1953 2,732,298 Stookey Jan.'24, 1956 OTHER REFERENCESLevy et al.: The Sylvania Technologist, July 1953, pages -63.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noa2,904,432 September 15, 1959 Eoward 01; Ross et al It is herebycertified that error appears in the -prinbed specification of the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 3, lines 3'7 and 38, strike out "of photo resist in theconventional manner by exposing the ooating"g column 2 line 3A, for,"referable reed preferable e Signed and sealed. this 29th day of March1965).

(SEAL) Attest:

KARL TLAXZINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

1. THE METHOD OF PRODUCING A PERMANENT, TWO-DIMENSIONAL, PHOTOGRAPHICIMAGE IN GLASS, WHICH COMPRISES FORMING DIRECTLY IN CONTACT WITH ASILICATE GLASS ARTICLE CONTAINING AN ALKALI METAL OXIDE A CONTINUOUSMETALLIC FILM OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTINGOF SILVER AND COPPER IN A PATTERN CORRESPONDING TO THE DESIRED IMAGE,HEATING THE ARTAICLE UNDER OXIDIZING CONDITIONS IN AIR AT A TEMPERATUREAND FOR A TIME SUFFICIENT TO OXIDIZE AND IONIZE THE METAL IMAGE AND TOCAUSE MIGRATION OF THE IONS INTO THE GLASS IN EXCHANGE FOR THE ALKALIMETAL IONS THEREIN, AND HEATING THE ARTICLE IN A REDUCING ATMOSPHERE TOREDUCE THE MIGRATED IONS TO METALLIC PARTICLES DISPERSED IN AND COLORINGTHE SURFACE OF THE GLASS.